NEW NORMAL: Scientists say a return to previous Arctic conditions is unlikely Image: U.S. Geological Survey

Warming continues to shrink the snow and ice cover that defines the Arctic, signaling the region’s shift to a new climate pattern, scientists said yesterday.

The area covered by sea ice hovered near its historic low this summer. In Greenland, record-high temperatures this year have helped accelerate the melting of the country’s massive ice sheet. Throughout the Arctic, permafrost is warming and the blanket of snow is shrinking.

Those changes appear to be long-lasting, said an international team of climate experts who wrote the National Oceanic and Atmospheric Administration report.

Its blunt headline? "Return to previous Arctic conditions is unlikely."

"The Arctic is a system, and the system is changing," said Don Perovich, a sea ice expert with the U.S. Army Corps of Engineers who worked on the report. "It’s not just that sea ice is being reduced. There’s changes in Greenland, the atmosphere, the ecosystem, and these changes are affecting human activity."

That includes densely populated areas of the globe that lie outside the Arctic.

More cold air blasts head south

The polar region acts as the world’s air conditioner, helping to regulate weather patterns worldwide. Now there is evidence that Arctic warming is affecting conditions in other regions of the globe, said NOAA oceanographer Jim Overland.

The unusually heavy snows that blanketed the eastern United States, northern Europe and parts of Asia last winter were a consequence of the shift to a warmer Arctic, he said.

"This connection was one of the real surprises that we’ve seen over the last decade or so," he said. "Normally, the cold air is bottled up in the Arctic, but we had two experiences last year where rather than winds blowing from west to east, they strongly blew from north to south. So first last December and then last February, we actually had cold air blowing from north of Alaska and in northern Canada blowing all the way in the central eastern U.S."

The seeming paradox of Arctic warmth sending blizzards to mid-latitudes has occurred just three times in the past 160 years, including last year. But it is likely to become more common as polar sea ice shrinks, Overland said.

That’s due in part to a powerful feedback loop scientists call "polar amplification." Warmer Arctic springs and summers increase the amount of sea ice that melts each summer, leaving huge swaths of dark ocean water that trap heat. That warmth cycles back into the atmosphere each fall, when the amount of sunlight dips and sea ice re-forms.

Meanwhile, historic warming observed in Greenland this year has implications for sea level rise, said Jason Box, an Ohio State University glaciologist who also worked on the new report.

Conditions have been warmer this year in Greenland’s capital, Nuuk, than at any other time since record-keeping began there in 1873.

The effects of that heat are evident in the behavior of the glaciers that connect Greenland’s massive ice sheet with the sea, Box said.

The massive Petermann Glacier calved a chunk four times the size of Manhattan in August, the largest single glacier area loss ever recorded in Greenland. But it was not an isolated event. Box says three other glaciers lost more than 10 square miles of area this year, and Greenland’s ice sheet is melting faster than it has since at least 1958.

"There is no doubt that Greenland ice loss has not just increased above past decades, but it has accelerated," Box said. "The implication is that sea level rise estimates will again need to be revised upward."